This invention relates generally to organic matrix composite structures coated with thermal oxidative barrier coatings.
Organic matrix composites (OMCs) such as PMR-15 and AFR-PE-4 are used in the aerospace industry for the weight reductions they offer when used to replace metal components. However, exposure to high temperature environments reduces mechanical properties and causes oxidative degradation of OMCs. Thus, improvements in high temperature properties of OMCs are sought.
One attempt to combat the problems encountered in the art is to build thicker parts. However, the increased thickness adds weight and cost to the component as compared to what could be achieved if thermal and oxidative effects on the component were reduced.
Another attempt utilizes a sacrificial layer on the component to retard material degradation. The sacrificial layer may be a thin carbon veil impregnated with the OMC resin. However, the protection provided by the sacrificial layer is lost over time.
Another approach is to formulate polyimide resins for use in OMCs to improve the service capabilities. However, polyimide resins generally present processing challenges and health concerns. In particular, partially unreacted solutions of a commercially available polyimide, PMR-15, include 4,4′-methylenedianiline (MDA), a known carcinogen and liver and kidney toxin.
Currently, there are investigations into the use of ceramic fillers carried in polyimide matrices applied as a thermally sprayed coating for OMC components. The coating purports to improve the environmental durability and erosion resistance of the organic matrix composites. However, the thermal spraying process raises environmental, health, safety, energy, and labor issues. Additionally, it is difficult to provide a fully-cured coating system during a thermal spraying deposition process.
Accordingly, it would be desirable to improve the high temperature performance of components comprising OMCs by providing a substrate/coating system with a two-pronged approach. The first prong is to provide a resin system for use in OMCs that overcomes current challenges. The second prong is to provide a compatible coating system for the OMC that improves thermal oxidative stability and mechanical performance.